An error compensation scheme is used to secure communication reliability. Examples of the error compensation scheme include a forward error correction (FEC) scheme and an automatic repeat request (ARQ) scheme. In the FEC scheme, errors in a receiving end are corrected by attaching an extra error correction code to information bits. The FEC scheme has an advantage in that time delay is small and no information is additionally exchanged between a transmitting end and the receiving end but also has a disadvantage in that system efficiency deteriorates in a good channel environment. The ARQ scheme has an advantage in that transmission reliability can be increased but also has a disadvantage in that time delay occurs and system efficiency deteriorates in a poor channel environment.
A hybrid automatic repeat request (HARQ) scheme is a combination of the FEC scheme and the ARQ scheme. In the HARQ scheme, it is determined whether an unrecoverable error is included in data received by a physical layer, and retransmission is requested upon detecting the error, thereby improving performance.
If the error is not detected from the received data, a receiver transmits a positive-acknowledgement (ACK) signal as a reception acknowledgement to report to a transmitter that reception is successful. If the error is detected from the received data, the receiver transmits a negative-acknowledgement (NACK) signal as the reception acknowledgement to report to the transmitter that the error is detected. The transmitter can retransmit the data upon receiving the NACK signal.
In a typical wireless communication system, only one carrier is considered even if a bandwidth between an uplink and a downlink is configured differently from each other. The carrier is defined with a center frequency and a bandwidth. A multiple carrier system uses a plurality of component carriers having a smaller bandwidth than a full bandwidth.
Long term evolution (LTE) based on 3rd generation partnership project (3GPP) technical specification (TS) release 8 is a most dominant next mobile communication standard.
The 3GPP LTE system supports only one bandwidth (i.e., one carrier) among {1.4, 3, 5, 10, 15, 20} MHz. In order to support a full bandwidth of 40 MHz, the multiple carrier system uses two carriers having a bandwidth of 20 MHz or uses 3 carriers respectively having bandwidths of 20 MHz, 15 MHz, and 5 MHz.
The multiple carrier system can support backward compatibility with respect to legacy systems, and significantly increases a data rate by using multiple carriers.
Even if a plurality of component carriers are supported, a base station (BS) and a user equipment (UE) do not use all component carriers in communication. The BS and the UE use assigned component carriers in communication among a plurality of component carriers.
For effective management of the multiple carriers, the BS and the UE can remove/change/add the assigned component carriers. However, a method of processing HARQ currently being performed has not been introduced for a case where a component carrier in which HARQ is currently being performed is removed or changed. When HARQ is suspended as the component carrier is transferred, the receiver has no choice but to discard previously received data, which may lead to inefficiency.